This proposal aims to establish a molecular link between G protein-coupled adenosine receptors (ADORs) and Fce/yRs on mature human mast cells to help explain the impact of adenosine on human allergic diseases such as asthma. Extracellular adenosine (extADO) is a purine nucleoside that when inhaled causes bronchospasm and enhances degranulation of mast cells in human asthmatic (but not in normal) airways. Thus, it is implicated in asthma pathogenesis. Four G protein-coupled adenosine receptors (A1AR, A2aAR, A2bAR and A3AR) have been identified and characterized. However, the ADOR responsible for the effect of extADO on human airway mast cells is not clear, though indirect evidence suggests A2bAR is involved. Two types of human mast cells, MCTC and MCT, have been described. MCTC cells from skin express tryptase, chymase, carboxypeptidase A3 and cathepsin G; whereas MCT cells express tryptase alone and are the predominant type in lung. Our preliminary data reveal that high extADO (10-4 M) inhibits FceRI-mediated degranulation of MCTC (skin) mast cells, whereas low extADO (10-7 M) augments mediator release from the MCT (lung) mast cells. Thus, indicating that extADO differentially regulates mediator release from these distinct types of human mast cells. extADO also augments secretion of IL-13, a Th2 cytokine implicated in asthma pathogenesis, but inhibits production of PGD2, TNF a, GM CSF and IL 6 from MCTC cells and inhibits NF-KB activation. The proposed research will characterize the effect of extADO on mediator release from the MCTC and MCT types of mast cells activated through FceRI and also FcyRlla, an activating IgG receptor recently discovered in this lab to be constitutively expressed on skin MCTC and, possibly, on lung MCT cells, and identify the ADOR(s) responsible for the observed contrasting effects on these two types of human mast cells. Syk kinase and src tyrosine kinases Fyn and Lyn, key regulators of FceRI-dependent degranulation, will be analyzed as targets of ADOR signals in MCTC and MCT mast cells. Repression of NF-KB activation will also be assessed as a general mechanism for IL-13 production. Allergies and asthma are major health concerns in the United States. Understanding the cellular components of these disorders and the molecular mechanisms that regulate these cell types is of prime interest in our efforts to alleviate the personal and societal burdens due to these disorders. (End of Abstract)